1. Field of the Invention
The present invention relates to a two-sided clamp for placing heads on the ends of paper rolls.
2. Description of the Prior Art
In the wrapping of paper rolls the inner heads are first placed onto the ends of each roll, after which a sufficient length of the wrapper is placed about the roll and then the overlaps of the wrapper are crimped over the rims of the inner heads. Conventionally, using a hot-melt glue, the outer heads are then adhered to the ends of the roll, thus covering the crimped edge of the wrapper and the inner head. The inner head is usually relatively thick and thus capable of protecting the roll end against mechanical damage. The outer head can thus be thinner serving the purpose of binding the wrapper at the roll ends and protecting the roll against humidity. Frequently, the coloring and printed pattern of the outer head are designed to give the roll a neat appearance.
The heads can be placed on the roll ends in a number of different ways. Manual placement of the heads is the oldest method, and it is still suitable for relatively small-capacity wrapping lines or applications not requiring an improved degree of automation. Here, the operator simply places the inner heads manually to the roll ends and the corresponding outer heads onto heated press platens, which next press the outer heads to adhere to the roll ends. The inner heads are held against the roll ends by means of separate retaining arms for the duration of the crimping of the wrapper overlaps against the roll ends. The adherence of the outer heads on the platens is in turn implemented with the help of a vacuum.
Various kinds of automatic heading machines have long been in use and several different types of such equipment are-known. A common feature for almost all automatic heading equipment is that, for each end of the roll, a separate apparatus with a head clamp is provided that serves for moving the head from the head pile to the roll end. In a prior-an heading machine, a rotatable arm is mounted on a vertical guide, and has at its end a rotatable vacuum clamp for grasping the heads. Such a heading machine is conventionally used in conjunction with different kinds of head storage shelves situated beside the heading machine. Using this machine, the heads are placed on the roll end so that the support arm of the clamp is transferred along the vertical guide to the level of the shelf containing the correct head size. Next, the support arm of the clamp and the heading machine itself are rotated until the machine is aligned parallel with the shelf. Subsequently the head is picked and transferred from the shelf to the roll end by rotating both the arm and the heading machine and moving the heading machine along the guide.
In another system, the heads are placed stacks or in piles on the factory hall floor and are transferred to the roll ends by means of gantry heading manipulators. The gantry transfer carnage is constructed above the head piles, and the heading manipulators are generally placed on a single, crosswise movable rail. Thus, a separate pile of heads of a predetermined size must be provided for each heading manipulator.
A major drawback of the above-described systems is in that a separate heading machine plus a dedicated head storage shelf or head pile is required for both of the roll ends. The heading machines employed are specifically built for manipulating heads only, whereby their control software is tailored particularly for each operating environment. Therefore, modifications to the operation of the system are cumbersome and require specialized design capabilities.
To overcome these impediments, a standard industrial multi-axis robot can be employed for placing the heads. Such a robot can be integrated with the layout of the wrapping line in a manner permitting the robot to place a head on both ends of the roll. For effective use of the robot, it must be provided with a two-sided clamp which through a flipping movement of the clamp is capable of sequentially picking heads for both roll ends, whereby the need for two separate head-fetching cycles is obviated. However, a conventional two-sided clamp is generally unsuitable for placing the inner heads. Namely, when the inner head is placed against the roll end, a retaining arm is first rotated against the inner head to hold it against the roll end. Now, if a two-sided clamp would be used in which both of the fetched heads are aligned to the same axis of the clamp, the head-retaining arm would first hit the head on the side outward from the roll end causing damage to the head or its detachment from the vacuum clamp. Moreover, the retaining arm could not rotate against the head placed at the roll end, whereby the already placed head would resultingly detach from the roll end.
For the above-described reasons, the clamp must be provided with a mechanism capable of transferring at least one of the suction head members of the clamp so that the suction head members are displaced asymmetrically thus permitting the head-retaining arm to freely rotate against the head already placed at the roll end. Such a mechanism can be implemented by means of a guide rail and a transfer motor, or alternatively, different types of lever mechanisms.
Obviously, the implementation of such a transfer mechanism in a clamp is a most demanding task. The clamp of the robot arm should offer maximum operational reliability and light weight, because the mass of the clamp directly affects the available payload capacity, operating speed and accuracy of the system. The additional mechanisms contribute to the mass of the clamp and require separate wiring for power feed and control. The routing of conductors to the clamp of the robot arm is obviously a difficult task. Thus, the implementation of a relatively simple transfer mechanism in a clamp may lead to significant technical problems. It must be further noted that the transfer mechanism brings about an additional axis to the system which complicates the adaptation of the robot software to the operating environment and adds to the programming work.